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1.
J Am Chem Soc ; 141(45): 17995-17999, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31647653

RESUMO

Hydrogen is regarded as an attractive alternative energy carrier due to its high gravimetric energy density and only water production upon combustion. However, due to its low volumetric energy density, there are still some challenges in practical hydrogen storage and transportation. In the past decade, using chemical bonds of liquid organic molecules as hydrogen carriers to generate hydrogen in situ provided a feasible method to potentially solve this problem. Research efforts on liquid organic hydrogen carriers (LOHCs) seek practical carrier systems and advanced catalytic materials that have the potential to reduce costs, increase reaction rate, and provide a more efficient catalytic hydrogen generation/storage process. In this work, we used methanol as a hydrogen carrier to release hydrogen in situ with the single-site Pt1/CeO2 catalyst. Moreover, in this reaction, compared with traditional nanoparticle catalysts, the single site catalyst displays excellent hydrogen generation efficiency, 40 times higher than 2.5 nm Pt/CeO2 sample, and 800 times higher compared to 7.0 nm Pt/CeO2 sample. This in-depth study highlights the benefits of single-site catalysts and paves the way for further rational design of highly efficient catalysts for sustainable energy storage applications.

2.
Nano Lett ; 19(8): 5388-5393, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31306028

RESUMO

We present a new methodology that enables studies of the molecular structure of graphene-liquid interfaces with nanoscale spatial resolution. It is based on Fourier transform infrared nanospectroscopy (nano-FTIR), where the infrared (IR) field is plasmonically enhanced near the tip apex of an atomic force microscope (AFM). The graphene seals a liquid electrolyte reservoir while acting also as a working electrode. The photon transparency of graphene enables IR spectroscopy studies of its interface with liquids, including water, propylene carbonate, and aqueous ammonium sulfate electrolyte solutions. We illustrate the method by comparing IR spectra obtained by nano-FTIR and attenuated total reflection (which has a detection depth of a few microns) demonstrating that the nano-FTIR method makes it possible to determine changes in speciation and ion concentration in the electric double and diffuse layers as a function of bias.

3.
J Am Chem Soc ; 140(47): 16237-16244, 2018 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-30369234

RESUMO

Knowledge of the molecular composition and electronic structure of electrified solid-liquid interfaces is key to understanding elemental processes in heterogeneous reactions. Using X-ray absorption spectroscopy in the interface-sensitive electron yield mode (EY-XAS), first-principles electronic structure calculations, and multiscale simulations, we determined the chemical composition of the interfacial region of a polycrystalline platinum electrode in contact with aqueous sulfuric acid solution at potentials between the hydrogen and oxygen evolution reactions. We found that between 0.7 and 1.3 V vs Ag/AgCl the electrical double layer (EDL) region comprises adsorbed sulfate ions with hydrated hydronium ions in the next layer. No evidence was found for bisulfate or Pt-O/Pt-OH species, which have very distinctive spectral signatures. In addition to resolving the long-standing issue of the EDL structure, our work establishes interface- and element-sensitive EY-XAS as a powerful spectroscopic tool for studying condensed phase, buried solid-liquid interfaces relevant to various electrochemical processes and devices.

4.
Sci Rep ; 8(1): 3125, 2018 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-29449590

RESUMO

Atomic force microscopy is used to conduct single-asperity friction measurements at a water-graphite interface. Local mapping of the frictional force, which is based on the degree of the cantilever twisting, shows nearly friction-free when a tip scans over a nanobubble. Surprisingly, apart from being gapless, the associated friction loop exhibits a tilt in the cantilever twisting versus the tip's lateral displacement with the slope depending on the loading force. The sign of the slope reverses at around zero loading force. In addition, the measured normal and lateral tip-sample interactions exhibit unison versus tip-sample separation. Theoretical analysis, based on the balance of forces on the tip originated from the capillary force of the nanobubble and the torsion of the cantilever, offers quantitative explanations for both the tilted friction loop and the unison of force curves. The analysis may well apply in a wider context to the lateral force characterization on cap-shaped fluid structures such as liquid droplets on a solid substrate. This study further points to a new direction for friction reduction between solids in a liquid medium.

5.
Langmuir ; 32(43): 11164-11171, 2016 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-27308947

RESUMO

The contact of water with graphene is of fundamental importance and of great interest for numerous promising applications, but how graphene interacts with water remains unclear. Here we used atomic force microscopy (AFM) to investigate hydrophilic mica substrates with some regions covered by mechanically exfoliated graphene layers in water. In water containing air gas close to the saturation concentration (within ∼40%), cap-shaped nanostructures (or interfacial nanobubbles) and ordered-stripe domains were observed on graphene-covered regions but not on pure mica regions. These structures did not appear on graphene when samples were immersed in highly degassed water, indicating that their formation was caused by the adsorption of gas dissolved in water. Thus, atomically thin graphene, even at a narrow width of 20 nm, changes the local surface chemistry of a highly hydrophilic substrate. Furthermore, surface hydrophobicity significantly affects gas adsorption, which has broad implications for diverse phenomena in water.

6.
Sci Rep ; 6: 24651, 2016 Apr 19.
Artigo em Inglês | MEDLINE | ID: mdl-27090291

RESUMO

Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces. Here, during advanced atomic force microscopy of the initial evolution of gas-containing structures at a highly ordered pyrolytic graphite/water interface, a fluid phase first appeared as a circular wetting layer ~0.3 nm in thickness and was later transformed into a cap-shaped nanostructure (an interfacial nanobubble). Two-dimensional ordered domains were nucleated and grew over time outside or at the perimeter of the fluid regions, eventually confining growth of the fluid regions to the vertical direction. We determined that interfacial nanobubbles and fluid layers have very similar mechanical properties, suggesting low interfacial tension with water and a liquid-like nature, explaining their high stability and their roles in boundary slip and bubble nucleation. These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis. The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules.

7.
Sci Rep ; 4: 7189, 2014 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-25424443

RESUMO

The thermodynamic properties of gases have been understood primarily through phase diagrams of bulk gases. However, observations of gases confined in a nanometer space have posed a challenge to the principles of classical thermodynamics. Here, we investigated interfacial structures comprising either O2 or N2 between water and a hydrophobic solid surface by using advanced atomic force microscopy techniques. Ordered epitaxial layers and cap-shaped nanostructures were observed. In addition, pancake-shaped disordered layers that had grown on top of the epitaxial base layers were observed in oxygen-supersaturated water. We propose that hydrophobic solid surfaces provide low-chemical-potential sites at which gas molecules dissolved in water can be adsorbed. The structures are further stabilized by interfacial water. Here we show that gas molecules can agglomerate into a condensed form when confined in a sufficiently small space under ambient conditions. The crystalline solid surface may even induce a solid-gas state when the gas-substrate interaction is significantly stronger than the gas-gas interaction. The ordering and thermodynamic properties of the confined gases are determined primarily according to interfacial interactions.

8.
J Phys Condens Matter ; 25(18): 184010, 2013 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-23598995

RESUMO

We have imaged nanobubbles on highly ordered pyrolytic graphite (HOPG) surfaces in pure water with different atomic force microscopy (AFM) modes, including the frequency-modulation, the tapping, and the PeakForce techniques. We have compared the performance of these modes in obtaining the surface profiles of nanobubbles. The frequency-modulation mode yields a larger height value than the other two modes and can provide more accurate measurement of the surface profiles of nanobubbles. Imaging with PeakForce mode shows that a nanobubble appears smaller and shorter with increasing peak force and disappears above a certain peak force, but the size returns to the original value when the peak force is reduced. This indicates that imaging with high peak forces does not cause gas removal from the nanobubbles. Based on the presented findings and previous AFM observations, the existing models for nanobubbles are reviewed and discussed. The model of gas aggregate inside nanobubbles provides a better explanation for the puzzles of the high stability and the contact angle of surface nanobubbles.


Assuntos
Grafite/química , Processamento de Imagem Assistida por Computador , Microbolhas , Microscopia de Força Atômica/métodos , Nanopartículas , Água/química , Propriedades de Superfície
9.
Langmuir ; 28(35): 12691-5, 2012 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-22897342

RESUMO

It was numerically predicted that dissolved gas particles could enrich and adsorb at hydrophobic-liquid interfaces. Here we observe nucleation and growth of bright patches of ∼0.45 nm high on the graphite surface in pure water with frequency-modulation atomic force microscopy when the dissolved gas concentration is below the saturation level. The bright patches, suspected to be caused by adsorption of nitrogen molecules at the graphite-water interface, are composed of domains of a rowlike structure with the row separation of 4.2 ± 0.3 nm. The observation of this ordered adlayer might underline the gas segregation at various water interfaces.


Assuntos
Carbono/química , Grafite/química , Interações Hidrofóbicas e Hidrofílicas , Microscopia de Força Atômica , Nitrogênio/química , Água/química , Adsorção , Propriedades de Superfície
10.
J Hazard Mater ; 177(1-3): 692-6, 2010 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-20060642

RESUMO

Rice-straw burning is a common post-harvest practice on rice paddy land, which results in the accumulation of rice-straw ash (RSA) in paddy soil. Because the occurrence of RSA in soil may affect the fate and transport of contaminants, this study investigated the sorption of 3-chlorophenol (3-CP) on RSA and RSA amended soils to evaluate the sorptive properties of RSA in soils. The results showed that the sorption of 3-CP to RSA proceeds through a surface reaction rather than through partitioning and that the neutral form of 3-CP is preferentially sorbed to the surface when compared to the deprotonated anionic form of 3-CP. The addition of RSA to the soils enhanced the overall 3-CP sorption, indicating that RSA amendment may be applied to retard the movement of 3-CP in contaminated soils. As the RSA content in the soils was increased from 0% to 2%, the Langmuir sorption maximum of the soils increased from 18-80 to 256-274 mg kg(-1). Thus, RSA contributed more to the total sorption of the soils than other major components in the soils. Nonetheless, the 3-CP sorption of the soils containing RSA was less than the combination of pure RSA and the soils, thereby indicating that the 3-CP sorption of RSA was suppressed. This may be attributed to the competition of organic matter or other soil components for the surface binding sites of RSA.


Assuntos
Clorofenóis/isolamento & purificação , Poluentes do Solo/isolamento & purificação , Adsorção , Incineração , Oryza , Solo
11.
Nanotechnology ; 20(33): 335701, 2009 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-19636091

RESUMO

We report a reliable method for preparing a pure Ir single-atom tip by thermal treatment in oxygen. The atomic structure of the tip apex and its ion emission characteristics are investigated with field ion microscopy. We have shown that the Ir single-atom tip can be a good field ion emitter, capable of emitting a variety of gas ion beams, such as He+, H2+, N2+, and O2+, with high brightness and stability. In addition, this tip can easily be maintained and regenerated in vacuum, ensuring it has sufficient lifetime for practical applications.

12.
J Hazard Mater ; 147(1-2): 313-8, 2007 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-17276599

RESUMO

The removal of 3-chlorophenol (CP) from water by carbon derived from burning of rice straw was evaluated in this study. Rice straw was burned at 300 degrees C in the air to obtain rice carbon (RC). Scanning electron micrographs showed a highly porous structure of RC. NMR and FTIR spectroscopy suggested an enhanced aromaticity of RC and the presence of oxygen-containing functional groups. Adsorption of CP by RC was characterized by L-shaped nonlinear isotherms, suggesting surface adsorption rather than partitioning. The adsorption occurred most strongly when CP existed as a neutral species. The adsorption decreased with increasing pH due to increased deprotonation of surface functional groups of RC and dissociation of CP. The adsorption capacity determined by data-fitting to the Langmuir model was 14.2, 12.9, 11.4 and 4.9 mg g(-1) at pH 4, 6, 8 and 10, respectively. These results suggest that rice-straw-based carbon may be effectively used as a low-cost substitute for activated carbon for removal of chlorophenols from water.


Assuntos
Carbono , Clorofenóis/isolamento & purificação , Oryza , Purificação da Água/métodos , Adsorção , Porosidade , Análise Espectral , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água
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